The San Rafael Swell is a large geologic feature known as an anticline or "dome". The San Rafael Swell
was formed when deeply buried Precambrian dike swarm rocks faulted,
or broke, during the Laramide orogeny, about 60 million years ago.
Since that time, the relentless force of running water and wind have eroded the geologic layers,
resulting in older rocks becoming exposed in the middle of the Swell,
and younger rocks exposed around the edges

Why you ask...should a mountain biker care about this geology lesson? Why indeed!

Picture this...flowing red rock sandstone (think Slickrock trail) steep walled slot canyons,
singletrack trails through juniper forests, views that resemble the Grand Canyon
and no people, cars or crowds! Just you, and hopefully some companions*, spending the entire day
mountain biking in one of the wildest regions in
North America! Without another person in sight!

* Keep safety first at all times in the 'Swell.' Think Aron Ralston and his "adventures" in this area.